Block copolymers containing polyoxymethylene units alongside other polymer and polycondensate units are described, for example, in JP 2007 211082 A, WO 2004/096746 A1, GB 807589, EP 1 418 190 A1, U.S. Pat. No. 3,754,053, U.S. Pat. No. 3,575,930, US 2002/0016395, and JP 04-306215.
U.S. Pat. No. 3,575,930 describes the reaction of dihydroxy-terminated paraformaldehyde HO—(CH2O)n—H having n=2-64 with diisocyanates to give isocyanate-terminated polyoxymethylene polymers, which can be converted to polyurethane compounds in the reaction with diols.
JP 2007 211082 A describes the reaction of polyoxyalkylene polyols having an equivalent weight of ≥2500 with formaldehyde, formaldehyde oligomers or formaldehyde polymers to give polyoxymethylene-polyoxyalkylene block copolymers using anionic or cationic polymerization catalysts. The high molecular weight polyoxyalkylene polyol starters having low polydispersity used are prepared via double metal cyanide (DMC) catalysis. Because of the high molecular weight of the polyoxyalkylene polyols, the resultant polyoxymethylene-polyoxyalkylene block copolymers have a molecular weight of at least >5000 g/mol and are therefore less widely usable as a polyurethane unit. Furthermore, the direct reaction of the polyoxyalkylene polyols with the polyoxymethylene polymers via a melt-kneading method necessitates the use of high temperatures and corresponding specific high-viscosity apparatus (extruders, kneaders, etc.).
U.S. Pat. No. 3,754,053 describes polyoxymethylene-polyoxyalkylene block copolymers having a molecular weight of ≥10 000 g/mol. For preparation of copolymers having an inner polyoxymethylene block, in a first step, trioxane is converted to a polyoxymethylene prepolymer and the latter is then reacted with alkylene oxides in the presence of NaOH, for example, as polymerization catalyst. Here too, the polymers described are not very suitable for uses as a polyurethane unit because of their high molecular weight.
WO 2004/096746 A1 and US 2006/0205915 A1 disclose the reaction of formaldehyde oligomers with alkylene oxides and/or isocyanates. In this method, by means of the described use of formaldehyde oligomers HO—(CH2O)n—H, polyoxymethylene block copolymers having a relatively narrow molar mass distribution of n=2-19 are obtained, but the provision of the formaldehyde oligomers proceeding from aqueous formalin solution requires an additional process step for thermal removal. The formaldehyde oligomer solutions obtained in this context are not storage-stable, and so they then have to be processed further immediately. Moreover, these applications do not disclose differentiated activation conditions, for example the activation temperature, of the alkoxylation catalysts used, which are disadvantageous from safety and quality-relevant aspects among others for any possible industrial scale application because of undefined temperature peaks during the exothermic polymerization process (22.7 kcal/mol PO from M Ionescu; Chemistry and Technology of Polyols for Polyurethanes Rapra Techn. Ltd., 2005). Furthermore, only block copolymers having very short formaldehyde blocks are obtainable via this method.
EP 1 870 425 A1 discloses a process for preparing polyoxyalkylene-containing polyols by condensation of substituted or unsubstituted phenol structures with formaldehydes and/or other substituted alkanal structures. The resulting phenol-formaldehyde condensates are used here as polyol starters for the alkoxylation, although no repeat oxymethylene units are formed within these starter compounds. In addition, resultant properties of the alkoxylated polyols containing aromatic systems differ fundamentally from aliphatic polyol structures because of the different chemical structures.
WO2012/091968 A1 claims a process for preparing polyetherols by polymerization of alkylene oxides onto starter compounds with the aid of DMC catalysts. In this case, the formaldehyde-associated structures disclosed are oligomeric phenol-formaldehyde condensates as corresponding starters, these differing fundamentally in structural terms from the polyoxymethylene starter structure.